The latest probe is likely to be exploited by Republican rival George W Bush, who has sought to turn controversy over 1996 Democratic campaign fundraising into a major issue in his race against Mr Gore.

Human errors

"The best campaign finance reform starts with having an administration that will adhere to the law and an Attorney General who will enforce the law," Mr Bush, who is campaigning in Florida, said.

"I look forward to seeing where these e-mails are and what was in these e-mails," he said.

The White House said it was co-operating with investigators, and officials deny that computer workers were threatened with jail if they disclosed what had happened.

One lawyer representing the White House said any mistakes were unintentional and the result of human errors.

She said reconstructing the e-mails could take three years and cost $3m.

The investigation was disclosed in court documents on Thursday.

The documents were filed in connection with a request that the court delay a civil suit over the e-mails, which was filed in part by the conservative legal group Judicial Watch, which has filed several lawsuits against the Clinton Administration.